The IBM PC family is based on the 8088, 80286 and 80386 Intel processors. A popular operating system for these PC's is the disk operating system ("DOS"). This operating system and all the applications that run under it are stored in the first 640 kilobytes of random access memory ("RAM"). (DOS 4.01 and earlier).
In order to speed up performance of DOS and DOS applications, many computer designers have installed memory caches on their systems. These systems typically use a small high speed memory as the "cache". This technique increases memory access speed when the program is loaded into the cache. This solution partially fails, however, when the size of DOS and the DOS applications exceeds the size of the cache memory. The system is then forced to wait to address data in the slower speed memories. Another disadvantage of cache memory systems are DRAM refresh delays. These delays are created by the need to periodically refresh dynamic RAM's. Because the caches are small and cannot contain entire DOS and DOS application data, they must be linked with the DRAM's. The DRAM's often contain spillover data from the cache. The cache memory then is idle while the DRAM's are refreshed.
It is one objective of the present invention to optimize performance of the memory containing the DOS and DOS applications.
This is a second objective of this inventor to have a zero wait state during memory reads and writes.
It is a still further objective of this inventor to avoid overhead involved in maintaining the slower dynamic random access memory ("DRAM") memory that contains the remaining system memory.